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PY3.1-12 | Nerve and Muscle Physiology — Practice Quiz
Practice
12 questions · Untimed · Unlimited attempts
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The resting membrane potential of a typical neuron is approximately -70 mV. This is closest to the equilibrium potential of which ion?
A
Na+ (E_Na = +61 mV)
B
K+ (E_K = -94 mV)
✓
C
Ca²+ (E_Ca = +123 mV)
D
Cl- (E_Cl = -76 mV)
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During the rising phase (depolarisation) of a nerve action potential, the membrane potential moves rapidly from -55 mV toward +30 mV. This is caused by:
A
Opening of voltage-gated K+ channels and K+ efflux
B
Activation of the Na+/K+-ATPase pump
C
Opening of voltage-gated Na+ channels and Na+ influx via positive feedback
✓
D
Closure of K+ leak channels and accumulation of intracellular K+
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A nerve conduction study shows a conduction velocity of 1.0 m/s. Based on the Erlanger-Gasser classification, this fibre is most likely:
A
Type Aα — motor to skeletal muscle
B
Type Aδ — fast pain and temperature
C
Type B — preganglionic autonomic
D
Type C — slow pain, postganglionic autonomic
✓
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A patient with Guillain-Barré syndrome has autoimmune destruction of Schwann cells in peripheral nerves. The primary physiological consequence is:
A
Loss of neurotransmitter synthesis in the neuron cell body
B
Disruption of saltatory conduction, severely reducing conduction velocity
✓
C
Destruction of nicotinic receptors at the neuromuscular junction
D
Depletion of acetylcholinesterase in the synaptic cleft
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At a chemical synapse, the entry of which ion into the presynaptic terminal is the essential trigger for neurotransmitter release?
A
Na+
B
K+
C
Ca²+
✓
D
Cl-
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A patient with myasthenia gravis has antibodies against nicotinic ACh receptors. After repeated nerve stimulation at 3 Hz, the compound muscle action potential (CMAP) shows a progressive decrease in amplitude (decrement). This occurs because:
A
ACh release from the motor neuron decreases with each stimulus
B
The reduced number of receptors causes the end-plate potential to fall below the safety factor with repeated stimulation
✓
C
The Na+/K+-ATPase cannot keep up with repeated action potentials
D
Myosin ATPase activity is directly inhibited by the antibodies
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In the cross-bridge cycle of skeletal muscle contraction, which step requires the binding of a new ATP molecule to the myosin head?
A
Formation of the cross-bridge (myosin binding to actin)
B
The power stroke (pivoting of the myosin head)
C
Detachment of the myosin head from actin
✓
D
Binding of Ca²+ to troponin C
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A muscle biopsy shows fibres that are rich in myoglobin, have abundant mitochondria, and are highly resistant to fatigue. These are most likely:
A
Type IIb (fast glycolytic) fibres
B
Type IIa (fast oxidative-glycolytic) fibres
C
Type I (slow oxidative) fibres
✓
D
Cardiac muscle fibres
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During fused (complete) tetanus, the muscle produces sustained maximal force because:
A
Each action potential is larger in amplitude than the previous one
B
Stimuli arrive faster than Ca²+ can be pumped back into the SR, maintaining high cytoplasmic Ca²+
✓
C
More motor units are recruited with each successive stimulus
D
ATP production increases with each contraction cycle
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A drug that inhibits myosin light chain kinase (MLCK) would most directly affect contraction in:
A
Skeletal muscle, because MLCK phosphorylates troponin
B
Cardiac muscle, because MLCK initiates Ca²+-induced Ca²+ release
C
Smooth muscle, because MLCK phosphorylation of myosin light chains is required to activate cross-bridge cycling
✓
D
All three muscle types equally, because MLCK is the universal contraction trigger
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The mechanism by which Ca²+ triggers contraction in cardiac muscle differs from skeletal muscle. In cardiac muscle, the process is called:
A
Direct mechanical coupling of DHPR to RyR1
B
Ca²+-induced Ca²+ release (CICR) via RyR2
✓
C
Calmodulin-dependent myosin phosphorylation
D
IP3-mediated Ca²+ release from the SR
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An athlete completes a 100-metre sprint in 10 seconds. During the first 8 seconds, the primary source of ATP for muscle contraction was:
A
Aerobic oxidative phosphorylation of fatty acids
B
Anaerobic glycolysis producing lactate
C
The phosphocreatine (PCr) system via creatine kinase
✓
D
Oxidation of branched-chain amino acids
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